1. Field of the Invention
The present invention relates to a composite magnetic material comprising a ferrite powder and a resin, and an inductor element constructed by using it. More specifically, it relates to a composite magnetic material and an inductor element advantageous for use in the electronic parts for high-frequency applications.
2. Description of the Related Art
In high-frequency circuits which are used for mobile communication devices including a portable telephone, a radio LAN, etc., an inductor element with a coil structure for covering the frequencies up to several GHz, such as a chip inductor, is used for the purposes of impedance matching, resonance or for a choke.
However, the coil was prepared by winding a wire around a core made of a non-magnetic material or by forming a coil pattern on a non-magnetic material, and thus it was necessary to have a large number of coil winding turns so as to obtain a desired impedance, resulting in a restraint toward the development of miniaturization. Since the resistance of the winding increases with increasing number of winding turns, there was also a problem that an inductor with a high Q (gain) could not be obtained.
To solve these problems, inductors having, as a core, a ferrite for high-frequency use, have been also investigated. By using a ferrite core, it is possible to decrease the number of coil winding turns in accordance with the permeability of the core material, and to realize miniaturization. However, a ferrite sintered body has a frequency relaxation phenomenon derived from magnetic domain wall motion, and a high Q can be maintained only when the frequency is restricted to a value up to about 300 MHZ at the most, even if a ferrox planer type ferrite sintered body (which is believed to have the most excellent high-frequency properties) is used.
It is therefore an object of the present invention to provide a magnetic material which has a larger permeability in comparison with a non-magnetic material in a frequency band of from several MHZ to several GHz, and can maintain a relatively high gain Q up to a frequency band of several GHz.
Another object of the present invention is to provide an inductor element which can be miniaturized and still can provide a high Q, by using the magnetic material described above.
The composite magnetic material comprises a ferrite powder and a resin, and the said ferrite powder comprises a spinel type ferrite including at least Ni and Co.
It is preferable that the ferrite is a spinel type ferrite having a composition represented by (NiO)x(CoO)y(MeO)z(Fe2O3)1xe2x88x92xxe2x88x92yxe2x88x92z, wherein Me is at least one selected from the group consisting of Mg, Cu and Zn, and x, y and z each satisfy the following conditions:
0.10xe2x89xa6xxe2x89xa60.550;
0.025xe2x89xa6yxe2x89xa60.200;
0xe2x89xa6zxe2x89xa60.200; and
0.400xe2x89xa6(x+y+z)xe2x89xa60.600.
The composite magnetic material is suitably applied to an inductor element.
According to the present invention, a composite magnetic material can be obtained which can provide a relatively large permeability in the frequency band of from several MHZ to several GHz, and which can maintain a high gain Q up to a GHz range.
Therefore, an inductor element constructed by using this composite magnetic material as a magnetic member, can realize miniaturization as well as a high Q.
For the purpose of illustrating the invention, there is shown in the drawings several forms which are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.